, Volume 138, Issue 1-4, pp 199-209

Adsorption of Copper in the Different Sorbent/Water Ratios of Soil Systems

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Abstract

While sorbate/sorbent, sorbate/water, and sorbent/water (S/W)ratios in a batch system are known to affect the adsorption ofsorbate, the effect of different S/W ratios on the adsorptionof inorganic sorbates has seldom been addressed. This studyinvestigates the adsorption phenomena of Cu2+ in differentsorbate/sorbent/water ratios in a batch system. Batch experimentsare performed to examine the adsorption, and the linear (K D), Langmuir (K L), and Freundlich (K F) adsorption coefficients of Cu2+ in lateritic soil. These experiments are conducted using solutions with initial concentrations of 0.5 to 50 mg Cu2+ L-1 equilibratedwith an appropriate amount of soil to give S/W ratios of 0.1 to 2 g mL-1. Although the variations in the sorbed amountand adsorption coefficients apparently originate from a changein the sorbate/sorbent/water ratio, only the equilibrium concentration significantly affects adsorption. On the otherhand, the linear and Langmuir isotherm cannot adequately describethe adsorption data. In this study, the Freundlich equation gavean excellent fit to the adsorption data with a goodness-of-fit(R2) > 0.984. However, adsorption isotherms should be regarded as only a curve-fitting model or a mathematical tool and cannot be employed to interpret any particular adsorptionmechanism. Meanwhile, the solids effect reveals that K F andmaximum adsorption (b) of the Langmuir equation increase when S/W ratio decreases. The sorbate in the stagnant phase must beconsidered as part of the equilibrium concentration in the solidphase to avoid underestimating the sorbed amount at a lower S/Wratio and/or a higher sorbate concentration level.